The present invention is directed to the establishment of a leak tight or leak limiting joint between a base surface and a mating end surface of a hollow body. More particularly, the invention involves establishing effective seals on inclined and/or non-planar surfaces where a non-uniform or asymmetric preload force is applied to a compression gasket. Typical of the use of such a joint would be in connection with nuclear steam supply systems for power generation.
In boiling water nuclear reactors, control rods are driven upwardly through "nozzles" disposed in the lower portion of the reactor pressure vessel. The nozzles are supported by and are longer than "stub tubes" which are welded to the interior wall of the reactor vessel. Each nozzle is sealed to its associated stub tube by means of an annular weld between the nozzle and the stub tube upper end.
As fully described and illustrated in U.S. Pat. No. 4,826,217, leaks or leak paths may develop during the operation of a boiling water reactor. The apparatus for sealing the leaks illustrated in that patent includes an outer housing or hollow body which surrounds the stub tube/nozzle tube assembly and is generally coaxial therewith. A lower gasket means in the form of a packing ring is disposed between the hollow body at its end which mates with the reactor vessel and the vessel wall, which can be termed a base surface. The hollow body surrounds the leak or leak path to be sealed and the gasket means has a preload force applied by torquing a sealing nut against a spring washer at the top of the housing until sufficient pressure is provided to insure a good seal under vessel low pressure conditions. Reactor internal pressure generates a downward, i.e., a seating force on the lower gasket means, through the hollow body during reactor operation.
Because the base surface is an inclined and/or a nonplanar surface, an asymmetrical loading results from the action of the reactor coolant on the sleeve housing and the housing or hollow body has a tendency to slide upwardly along the inclined vessel wall or base surface. Such sliding movement could result in the loss of sealing at the joint between the base surface and the mating end surface of the hollow body.